Particularly in diagnostic medicine it is well established practice to use labelled species to bind to substances of interest (analytes) in order that the intensity of the original from the lable may be used to ascertain the presence or concentration of the analyte.
Such labelled species require two functional attributes--the first being the ability to produce a detectable signal, actively or passively, and the second being the ability to bind to a desired binding partner.
The signal forming attribute may conveniently be fulfilled by the presence in the labelled species of a reporter moiety or "label" which itself acts as a radiation emitter, absorber or modifier or which cooperates with another species to achieve a radiation emitting, absorbing or modifying effect. Thus for example the label may be a chromophore, a fluorophore, a radionuclide, or a material having detectable magnetic characteristics, e.g. paramagnetism, superparamagnetism etc.
One form of labelled species that has been proposed for diagnostic use, e.g. in assay lists, fulfills the binding ability attribute by the inclusion in the species a --B(OH).sub.2 or --B(OH)3--binding group.
Such boronic acid conjugates have the ability to bind to cis-diols, e.g. in proteins. By way of example, boronic acid conjugates of this nature are described in WO-92/08722, US-A-4659817, DE-A-3720736 and US-A-4861728. The compounds described there comprise antibody or chromophoric or fluorophoric label moieties. Such compounds are useful in assays for glycated blood proteins in view of their ability to bind to the glycosyl moieties. The labelled conjugates of WO-92/08722 are especially useful in this regard as the chromophores and fluorophores there described have absorption maxima above 600 nm and thus there is no interference between their spectral response and that of hemoglobin.
These labelled boronic acid conjugates can be represented by the general formula I EQU V-W-B(OH).sub.2 (I)
where V is a reporter moiety, e.g. a chromophore, fluorophore or radioisotope and W is a bond or linking organic group.
WO-92/08722, like other publications describing labelled boronic acid conjugates, suggested that the linker group, W in formula I above, might suitably incorporate a m-aminophenyl group attached to the boronic acid residue. Thus such compounds may readily be prepared by conjugating the label to m-aminophenyl-boronic acid thereby producing a compound of formula II ##STR2##
(where V is as defined above and W.sup.2 is a bond or an organic linker moiety).
Such compounds however have been found to have limited acceptability in terms of stability and water solubility and for certain assay procedures have necessitated the use of organic co-solvents such as DMSO, DMF and formamide rather than of water alone.